Exemplary embodiments of the present invention relate to an image sensor and an image data processing method using the same.
An image sensor refers to a semiconductor device which converts an optical signal into an electric signal. The image sensor is categorized into a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor. In the CCD image sensor individual MOS capacitors are disposed very close to each other and charge carriers are stored in the MOS capacitors. As for the CMOS image sensor, a pixel array including MOS transistors and photodiodes, a control circuit, and a signal processing circuit are integrated into a single chip.
The CCD image sensor has disadvantages in that a driving scheme is complicated, a large amount of power is dissipated, and a fabrication process is complicated because a large number of mask process steps are required. It is also difficult to achieve a one-chip implementation because a signal processing circuit cannot be integrated into a CCD chip. However, the CMOS image sensor reproduces an image by forming a photodiode and MOS transistors within a unit pixel and sequentially detecting signals in a switching scheme. The CMOS image sensor has advantages in that power dissipation is reduced and the number of masks is reduced in a fabrication process, as compared to a CCD process, thereby improving fabrication efficiency. In addition, a one-chip implementation can be achieved since several signal processing circuits and pixel arrays can be integrated into a single chip. Hence, the CMOS image sensor is considered as a next-generation image sensor.
In general, an image sensor includes a pixel array, which receives external incident light and converts photoelectric charges into electric signals, and micro lenses which are arranged in pixels on the pixel array. In addition, the image sensor includes a logic circuit which processes light sensed through the pixel array into electric signals and converts the electric signals into data.
Much research has recently been conducted to develop various methods for improving photosensitivity of the image sensor. One of these methods is to increase a fill factor which is defined as a ratio of an area occupied by a light sensing portion with respect to an entire image sensor. However, since the logic circuit part could not be fundamentally eliminated, such an effort has encountered a limit in a limited area.
Crosstalk is a representative noise component which degrades image reproduction quality of the image sensor. In the image sensor, crosstalk may occur in a region on which light is incident or may occur due to pixel arrangement of a pixel array.
It is ideal that 100% of light is incident on a photodiode region of the pixel. However, since several material layers, such as a multilayer interlayer dielectric layer, an overcoating layer (OCL), and a plurality of passivation layers, are present on the photodiode region, 100% of light is not incident on the photodiode region and a portion of light is incident onto an adjacent photodiode region.
In addition, it is usual that the pixel array is configured with a Bayer pattern which is most widely used. The Bayer pattern is characterized in that 50% green pixels, 25% red pixels, and 25% blue pixels are disposed. The red pixels and the green pixels are alternately disposed in a single line, and the blue pixels and the green pixels are alternately disposed in a next line. If the pixels are disposed in the above manner, the same green pixels can transfer a different amount of light for the same scene, depending on whether their adjacent pixel is the red pixel or the blue pixel. This is referred to as a Gb-Gr offset. Due to the Gb-Gr offset, a step-like noise component occurs in a finally reproduced image.